Image forming apparatuses such as printers, facsimiles and copiers are apparatuses which form images including letters, characters and symbols on recording media such as paper, cloth and OHP sheets based upon image information. Electrophotographic image forming apparatuses, in particular, are capable of forming high-definition images on plain paper at high speed, and so they are widely used in offices and the like. In such electrophotographic image forming apparatuses, thermal fixing methods are widely used in which toner on recording media is heated and melted and the melted toner is fixed onto the recording media by application of pressure. These thermal fixing methods are favorably used because they offer high fixing speed and high fixed image quality.
The power consumption in these electrophotographic image forming apparatuses is largely accounted for by the heating of the toner in the thermal fixing methods. In view of the tackling of environmental problems which has been attracting attention in recent years, there is much need for provision of low-power-consumption (energy-saving) fixing devices. Specifically, there is much need for provision of fixing methods for dramatically lowering the temperature at which toner is heated for its fixation, or fixing methods which do not necessitate heating toner. In particular, non-thermal fixing methods in which toner is fixed to recording media without heating the toner at all are ideal in that low power consumption can be achieved. Regarding the non-thermal fixing methods, those which use solvent have been proposed. However, since such fixing methods which use solvent involve swelling or melting toner, they present problems of offset and the remaining presence of tack in the non-thermal fixing methods.
To prevent the offset, various methods have been proposed. A first method is a method of improving separability of a surface layer of a fixing member by providing the surface layer with an offset-preventing layer made of a material which enables high separability. A second method is a method of improving separability of a fixing member by applying a release agent such as silicone oil to a surface layer of the fixing member. A third method is a method of applying to a fixing member a direct-current bias which has the same polarity as toner of an unfixed image borne on a recording medium and thus preventing attachment of the toner to the fixing member. A fourth method is a method of removing toner attached to a surface layer of a fixing member, by providing a certain rubbing cleaning unit. Further, there are methods of preventing the offset by combining these methods, etc. Also, hardening of ink by means of light or heat, coating with a member which enables separability, and the like have been proposed as methods of removing or reducing tack.
For example, PTLs 1 to 3 each propose a method, etc. which is a combination of the above-mentioned first method, the above-mentioned second method and other method(s) to prevent offset and the like. However, since the fixing methods described in these proposals are thermal fixing methods, the problems of offset and the remaining presence of tack in non-thermal fixation cannot be solved.
PTLs 4 and 5 propose methods of removing or reducing tack by hardening ink with ultraviolet light or heat. However, since the methods described in these patent literatures employ thermal fixing methods, the problems of offset and the remaining presence of tack in non-thermal fixation cannot be solved.
PTL 6 discloses a fixing solution enabled to reduce generation of additive odor, suppress disturbance to toner images and fix toner at high speed, by adding a specific water-soluble resin to the fixing solution; and a fixing device configured to fix toner, using the fixing solution. However, if the water-soluble resin described in this patent literature is added, the foamability and foam stability of a fixing solution degrade noticeably and thus it is impossible to obtain a foamy fixing solution.
PTL 7 proposes providing a foamy fixing solution to resin-containing fine particles such as toner particles on a medium such as paper. By doing so, it is possible to avoid disturbance to a fine resin particle layer on the medium, the fine resin particles are quickly fixed to the medium after the application of the fixing solution to the medium where the fine resin particles are attached, and further, the fixing solution can be applied in small amounts to such an extent that residual liquid is not felt on the medium. However, tack remains when an image portion is formed with the amount of the fixing solution applied being very large, for example when the amount of toner attached varies over the same sample.
In the case of color images, as opposed to the case of monochrome images, when grain boundaries exist between toner particles, light incident on toner layers scatters and thus it is difficult to exhibit the color reproducibility required for the fixed images. Means for exhibiting the color reproducibility include a means of increasing the amount of a fixing solution applied. However, if the amount of the fixing solution applied is increased, tack may possibly remain as mentioned above. This occurrence is noticeable in the case of color images where the amount of toner tends to be unevenly distributed. Accordingly, a fixing solution has been in demand which is capable of forming a uniform film-like fixed image, with the amount of the fixing solution applied being small and without creating grain boundaries between toner particles.